In the debate over moral bioenhancement, some object that biochemical, genetic, and neurological interventions aiming at enhancing moral agency threaten the autonomy of persons, as they compromise moral deliberation and motivation. Opponents of this view argue that such interventions may actually enhance autonomy itself, thereby increasing a person's capacity for moral agency. My aim is to explore the various senses of autonomy commonly appealed to in such controversies and to expose their limitations in resolving the central disputed issues. I propose (...) that a Kantian conception of autonomy is more effective in addressing these issues, as it specifies the key features that inform an intelligible account of moral worth and moral law. A consideration of these features is typically lacking in the arguments advanced by contenders in these debates. Guided by a Kantian framework, I argue that moral bioenhancement projects directed at affecting moral autonomy are not as promising as they appear, for both metaphysical and empirical reasons. (shrink)